Central nervous system (CNS) tumors exhibit a high degree of neovascularization. The neovascularization of these and other solid tumors has long been recognized as necessary for tumor growth and maintenance. Several lines of evidence indicate that tumor neovascularization is mediated by a humoral factor elaborated by the tumor, per se. We propose to use an in vitro model tissue culture system wherein human endothelial cells are the target of a trophic or vasopoliferative factor elaborated by tumor cells. Our previous work has shown that CNS tumor cells in culture elaborate a specific endothelial cell mitogen, termed by us "End thelial Proliferative Factor" (EPF). We propose to isolate and characterize this "EPF" from astrocytoma conditoned media, using the in vitro bioassay of endothelial proliferation. The astrocytoma cell line has been adapted to roller culture, which will insure the supply of large volumes of conditioned medium enriched in the endothelial mitogen. A long-term objctive of the proposal is the production of monospecific antisera to EPF.